Ultraviolet water and air purification and sterilization systems are known and have a successful history of development. The main unit of these ultraviolet systems is a source of ultraviolet radiation having wavelength(s) close to the absorption peaks of biologically significant molecules of DNA and proteins. The system can sterilize a medium to a safe condition providing the power of the ultraviolet source and an exposure time are sufficient to destroy the internal biomolecular structure of bacteria, viruses, protozoa and germs.
Known ultraviolet water and air sterilization systems use mercury lamps or deep UV light emitting diodes as a source of ultraviolet radiation. Low-pressure and medium-pressure mercury lamps provide a linear spectrum of radiation with some lines, which wavelengths are in the relative vicinity to a DNA absorption line. A low-pressure mercury lamp with a main peak at 253.4 nm often is used in low-consumption residential water and air purification systems. Medium-pressure mercury lamps with a higher radiation power have a multi-peak radiation spectrum and often are used in municipal systems with medium and high water consumption.
However, the use of mercury lamps has significant drawbacks. For example, mercury lamps are fragile and bulky and mercury is an extremely dangerous element, which implies serious limitations on applications of the mercury-based water purification systems. In particular, mercury lamps are not practical for use in transport and individual systems. Furthermore, a typical operating lifetime of a mercury lamp is less than 10,000 hours. An additional limitation is an inability to adjust or control a radiation spectrum of the mercury lamp. To this extent, the peaks of a mercury lamp do not exactly coincide with the absorption peaks of DNA and proteins, thereby decreasing the sterilization efficiency.
Some approaches have sought to minimize one or more drawbacks of mercury lamp-based sterilization. For example, one approach proposes a handheld ultraviolet water purification system based on a miniature mercury lamp. The design is targeted to overcome the size and portability drawbacks of traditional mercury lamp-based ultraviolet purifying systems. Nevertheless, the need for contact and even steering the sterilizing water with a fragile quartz sleeve with the mercury lamp inside makes the device dangerous for residential applications and not appropriate for transport, field, and portable applications.